Cathode ray tube device



Sept 4, 1956 w. H. BAKOW 2,761,989-

CATHODE RAY TUBE DEVICE Filed Feb. 28, 1955 IIA l Ilv Y .'N JNVENTOR. /lgzzmmfariw vb Qw produced by the phosphor areas.

United States Patent O CATHODE RAY TUBE DEVICE William Henry Barkow, Pennsauken, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application February 28, 1955, Serial No. 490,979 11 claims. (ci. sis-17o) This invention relates to systems for controlling the electron beams of cathode ray tubes and, particularly,

to systems in which a plurality of beams is deflected by a A Three-Gun Shadow-Mask Color Kinescope, by H. B. f

Law published in the Proceedings of the I. R. E., vol. 39, No. l0, October 1951 at page 1186. Such a tube has a luminescent screen as part of a target electrode in which different phosphor areas produce differently co1- ored light when excited by electron beam components impinging upon it from different angles, the angle of impingement determining the particular color of the light The invention also pertains to a kinescope of the type described in another article titled A One-Gun Shadow-Mask Color Kinescope, by R. R. Law, published in the Proceedings of the I. R. E., vol. 39, No. 10, October 1951 at page 1194.

It is necessary for the satisfactory operation of such kinescopes to effect substantial convergence of the different electron beam components at all points of the raster scanned thereby in the plane of the target electrode. In general, this convergence may be effected by means of apparatus such as that disclosed in an article titled Deection and Convergence in Color Kinescopes by A. W. Friend, published in the Proceedings of the I. R. E., vol. 39, No. 10, October 1951 at page 1249. Such beam convergence apparatus includes an electron-optical system by which to control the beam convergence angles. The electron-opticalv system is variably energized as a function of the-radial angle of beam deflection.

Another type of apparatus for controlling the convergence of a pluralty'of electron beam components in a predetermined plane and with which the present invention may be employed with particular advantage, comprises, in general, means for producing a plurality of lelectron beam components which traverse predeection paths that are spaced respectively about the longitudinal axis of the tube, and individual electromagnetic means located respectively adjacent to the predellection beam paths and of such a character as to be energizable directly from the beam deflection circuits in a manner to etect the desired beam convergence. In this manner, the beam convergence angle may be varied in a manner suitable to maintain the desired beam convergence in the predetermined plane at all points in the scanned raster.

More particularly, it will be understood thatthe term beam components as used herein denotes either a plurality' of individual electron beams emanating, respectively, from a plurality of electron guns or from a single jelectron gun provided with suitable electron-opticaLor other apparatus, for forming three individual beams and,

'in addition', those components of a single electron beam to which is imparted a spinning motion so as to trace a substantially conic locus at differentposition's thereof.

Accordingly, the apparatus by which a plurality ofsuch 2 electron beam components is produced may include on the one hand, three electron guns or, on the other hand, a single electron gun, together with the auxiliary apparatus by which the spinning motion is imparted to the beam.

One particular beam convergence apparatus with which this invention may be advantageously employed includes for each beam component a pair of pole pieces located internally of the kinescope envelope. It has been found that magnetic flux leaking from the deection yoke traverses the Various pairs of pole pieces differently, thereby tending to cause a misconvergence of the beam components. i

It is a primary object of the present invention to provide means for restraining the magnetic fields which ordinarily extend beyond an electromagnetic deflection yoke.

Another object of the invention is to present leakage ux from a raster-scanning deflection yoke from aiecting beam-convergence apparatus in a manner to cause rnisconvergence of a plurality of beam components.

Still another object of the invention is to shield a plurality of individual beam-convergence electromagnets located in a predeflection region of a plurality of beam components from a raster-scanning deflection yoke.

In accordance with the `disclosure in the H. L. Goodrich U. S. Patent No. 2,677,779, granted May 4, 1954, multi-beam cathode ray tube apparatus, having a plurality of beam convergence electromagnets located in a predeiiection region of the beams, is provided With a magnetic shield located between the beam deiiection apparatus and the beam convergence apparatus to exclude from the latter leakage'ux from the former. Such a shield may, as stated therein, Acomprise a disk of high-permeability material such as ferrite.

Since the horizontal frequency deflection eld is also capable of producing deleterious eects upon beamconvergence apparatus of that type, there is disclosed in the co-pending application of A. M. Morrell, S. N. 395,- 371, led December 1, 1953, a shield designed specifically for shielding against the ux produced by the high frequency deflection coils, which shield may be of conductive material such'as copper having no undesirable distorting effect upon the deflection yoke eld.

The present invention provides improved magnetic iluxpermeable means for' restraining primarily the low frequency vertical deflection ux which ordinarily extends rearwardly of the deilection yoke, which means will be understood as using lessv axial length of the cathode ray tube than prior' art devices'.v Moreover, the shielding means of the'- invention-aiotds more uniform shielding action and with substantially no undesirable effect upon lthe deection centers of the yoke fields.

In accordance with a specific form of the present invention, there is provided in conjunction with an electromagnetic deection yoke a conductive disk (e. g. copper) for shielding the high frequency deection ilux and a pair of grain-oriented steel disk-like members Whose respective directions of grain orientation are normal to each other. The conductive disk is most effective at the horizontal scanning frequency rate while the steel disks serve efficiently to restrain rearward activity by vertical deection ux.-

Additional objects and advantages of the present invention will vbecome apparent to persons skilled in the art from a's'tudy of the following detailed description of the accompanying drawing in which:

Figure l is a view showing the general arrangement of image-reproducing apparatus embodying an electron beam convergence system and including shielding means in accordance with one form of this invention;

Patented Sept. 4, 1956 ofthe screen 12.

3 arrangement of the beam convergence electromagnets illustrated in Figure l; and

Figure 3 is an enlarged, vertical sectional view of a portion of the apparatus of Figure 1 showingftheshielding apparatus more clearly.

Reference 'rst will be made to Figure 1 fou a general A description of au illustrative embodiment of .electron beam convergence system inV connectionV with. which the present invention inds particular application. rlhe system includes a tri-color kinescope 11 which. may be of. the same general type as that disclosed inthe H. B. Law paper previously referred' to. It will be' understood, however, that the kinescop'e, alternatively,l maybe of. other types such as that shown in the R..v Law paper. In either case, however, the kinescope preferably has a luminescent screen V12 provided with. a multiplicity of small. phosphor Cil areas arranged in groups andcapablerespectively of' producing light of the dileren'tprimary colors in: which the image is to be reproducedwhen excited by an electron beam. In back of and spaced from .the screen 12 there is an apertured masking electrode 13 having an aperture for andY in alignment with each group of phosphor areas In the particular tube illustrated, the kinescope also has a plurality of electron guns, equal in number to the number of primary colors in which the image is to be reproduced. Each of these guns may be conventional,

consisting of a cathode, a control grid, an `accelerating grid and a focusing electrode. Since thethree-gum are identical, the different parts thereof will be referred co1- lectively as the cathodes 1 4', the control. grids 14, accel` erating grids 15, and the focusing. electrodes 16. The three electron guns produce schematically represented beams 17, 18 and 19 by which to energize, respectively, the blue, red and green phosphor areas of thescreen 12. When these electron beams are properly converged'in the plane of the masking electrode 13, they lpass through the apertures thereof fromditerent directions and impinge upon ditterent phosphor areas of the various groups so as to produce blue, red and green light. It is to be noted that the size of the phosphor areas, the angles between the beams and the spacing of the mask 13 vfrom the screen 12 as compared with the length 'of the tube are exaggerated for better illustration of the operation vof the kinescope.

The electron-optical apparatus of the kinescope 11 also includes a beam-accelerating electrode consisting, in the present instance, of fa conductive wall coating 20 formed on the inner surface of the tubular neck 21 of the kinescope extending from the region adjacent to the. outer end of the electrodes 16 to the Vconical 'section 22 of .the tube t which in this case is metallic. Suitable electrical connection (not shown) is made at `thejunction V`of the w` l coating with the metal cone 22. A Cylinder 20 electrif cally connected to the wall coating 20 also serves inthe focusing of the several beams. Preferably, the target electrode structure, includingthe masking electrode 13 and the luminescent screen 12 which for this purpose may be metallized, is electrically connected to lthe .metal cone 22 by suitable means (not shown). Metallization of -a lunminescent screenof the character described .may be effected in the manner disclosed .in a Tpaper .by D, W. Epstein and L. Pensak titled Improved .Cathode Ray Tubes with Metal-Backed Luminescent Screens :published in the RCA Review, vol. VII, March 1946 at pages -10.

The described electrode structure .of the kinescope may e energized a conventional .manner vsuch .as that illustrated. The source of energyis .represented .by abattery 23 across the terminals of which there is .connected a voltage divider 24. The cathodes 14' 'areconnected .to a point which is somewhat negative relative 'to ground. The accelerating grids are supplied with'apotentialof, for example, 200 volts.l Similarly, 'th'efocusing electrodes V 16 are connected to a point on the -voltagedivider which may conventionally be at a potential of approximately 4 8G00 volts positive relative to the grounded cathodes. Also the beam-accelerating anode, including the wall coating 20 and metal cone 22, is connected to the voltage divider 24 at a point which may conventionally be approximately 27,000 volts positive relative to the grounded cathodes.

The electron beams 17, 118 and 19 are modulated suitably in intensityy under the control of color-representative video signals derived from a source 25. It will be understood that the video signal source isrepresented herein entirely diagrammatically since it doesv not form an essential part of the presentinvention. The signal source 25 usually'will bepart of asignal receiver and: maybe understood to include a signal detector, or equival-ent device, together with one or more stages of video signal amplification. Alternatively, the video signal source may be a color television camera in the event that the kinescope 11 is employed as a monitor, for example. Also, it willV be understood that the illustrated connectiony of the video signal source 2,5 tothe electron, guns of the kinescope 11 is merely diagrammatic and accordingly these connec-V tions, may or may not; be made directly to the cathodes 14. Instead, it will be understood, that they may be made to the grids 14 or, in accordance with modes of operation of color image-reproducing apparatus, the video signal source may be connected both to the cathodesand to the control grids of the electron guns.

Also associatedA with the color kinescope 11 is a de. Iection yoke 26 which may be entirely conventional including two pairs of suitably placed coils electrically connected together in such a manner that, when properly energized, electromagnetic fields are produced, W'Ilreby to etect both horizontal and vertical angular deections of the electron beams so as to scan the usual rectangular raster. lEnergization of the deection coils comprising the yoke 26 may be effected by conventional vertical and horizontal deflection wave generators 27 and 28, respectively. Such apparatus will be understood to function suitably to produce substantially Silwtooth energy at both horizontal and vertical dellection frequencies so that the fields produced by the yoke 26 are varied in a substantially sawtooth manner.

The beam convergence system also includes a plurality of electromagnetic lield producing .elements such as the magnets 29 and 30 mounted around the neck 2l .of the color kinescope adjacent to the predeection paths of the electron beam components. Itis to be unt erstood that the precise location of these magnets is not necessarily indicated in the figure. Instead, as will .appear in .greater detail, it is to be understood that each of these'magnets is located relative-.to .one of @the .electron beam co1 po ents so las 'to niunceits associated beam component to the substantial exclusion :ef the .others .Furthermore it .is to .he understood that. these magnets are `of ;a charapter which, when .suitably energized, produce ,rspecti-ve ilields which are .transverse to .theassociated beam paths.

Each of these .convergence.electromagnets rlludes a pair .of lspaced pole pieces .and at least .one energizing Winding. d Preferably two windings .are provided for each of the electromagnets for separate .energization These vfeatures will be .described subsequently in ygreater detail.

4Before,describing the details o f the .convergence system, .a brief description will ,begiven of .the.ger1er-al mannerin Awhich `the apparatus .functions Vto produce the ,desired results. Zlhe convergence .magnets su,cl1 as 2 9, a1 d, 3,0 are energized by substantially .unidirectional energy so .asito etect an .initialnonvergence of L the Af s/lectror; beam :components substantially in .,thergplane of the aperturerl masking-electrode 113. AIn .order to do the .unidirectional -energization .of .these :magnets .is .effected n way that .the magnets inlay be .finsliyldually ,energized `indifferentrnagnitudes. In QaCting initil beam iconvergencait is to be understood vthat ithe:beam,nraylge tin vany desired -one of their Adifferent -deflected positionsof the raster to be scanned. Alternatively they may be initially converged at one corner of the raster.

The convergence magnets such as 29 and 30 also are dynamically energized by the control wave energy derived from a suitable generator (not shown in Figure l) so as to effect a variation in the magnitude of the transverse iields produced respectively thereby. These eld strength variations are in accordance with a predetermined function of the beam deflection. Variations in the strength of the fields produced by the convergence magnets such as 29 and 30 eect corresponding variations in the paths of the electronbeam components relative to the longitudinal axis of the tube. Hence, suitable variations are made in the convergence angles between the various beam components substantially in the plane of the masking electrode 13.

For a further description of this type of beam convergence apparatus, reference now will be made to Figure 2 of the drawings. This figure shows more clearly the relative positions of the convergence magnets, such as 29 and 30 and, additionally, 31, relative to one another and to the electron beams with which they are respectively associated. Inasmuch as all of these magnets are substantially the same, only one of them will be described in detail. The convergence magnet 29, which is associated with the blue electron beam 17, is provided with a core having a body portion 32 and two external pole pieces 33 and 34. These pole pieces are mounted so as to be in close association with the tube neck 21. Also, as indicated in Figure 1,.the pole pieces extend for some distance longitudinally of the tube substantially as indicated. The magnet also is provided with an energizing coil structure 35 mounted upon the body portion 32. The energizing coil 35 preferably is provided with two windings, one for static energization and the other for dynamic energization. The convergence magnet 29 produces a field which, in the vicinity of the electron beam 17, is substantially transverse to the axis of the kinescope. By means of such a field, the electron beam 17 may be moved toward or away from the longitudinal axis. The direction and magnitude of such a beam movement is controlled by the energization of the magnet by means including the coil 35.

ln Figure 2, it also is illustrated that for each of the magnets there are provided on the inside of the tube neck 21 extended pole pieces so as to increase the effectiveness of these magnets. The magnet 29, for example, is provided with a pair of inwardly extending pole pieces 36 and 37, associated respectively with the external pole pieces 33 and 34. By such means, it is seen that the reluctance of the magnetic circuit is considerably decreased, and also the ux distribution of the eld produced between the internal pole pieces 36 and 37 is .considerably improved.

With beam convergence apparatus of this general character, it may be seen from a further consideration of Figure 2 that such apparatus is adversely efected by both horizontal and vertical deflection flux from the deflection yoke. Leakage dellection ilux of a character to deflect the electron beam components 17, 18 and 19 to the left as viewed in the drawing is indicated by the broken lines 3S. With respect to the internal pole pieces 36 and 37 associated with the electromagnet 29, no adverse eiects of the leakage dellection ux are produced. However, it is seen that the leakage deflection ux 38 passes between the internal pole pieces 39 and 40 of the electromagnet 30 substantially at right angles to these pole pieces since this is the path of lowest reluctance. Similarly, the leakage deflection ux 38'passe's between the internal pole pieces 41 and 42 of the electromagne't 31 at right angles to these pole pieces. As a result, it may be seen that when the beams are being ldeflected to the left, the red beam 18 will be moved to ahigher position than it would have in the absence of the leakage ux from the deection yoke, as indicated by the arrow. Similarly, the

aluminum or other non-magnetic material.

green beam 19 will have a lower than normal position when beam deflection is toward the left. Conversely, when beam deection by the yoke is toward the right, as viewed in Figure 2, the leakage llux 38 will be in the opposite direction, thereby tending to move the red beam downwardly and the green beam upwardly. Consequently, there is effected a misconvergence of the electron beam components as a result of the leakage flux from the deflection yoke traversing the internal pole pieces of certain of the convergence electromagnets.

As has been stated, the present invention provides new and improved means for restraining the activity of the deliection ux of the electromagnetic yoke 26 and in a manner which prevents the defiection flux from having an undesirable effect upon the convergence magnetic elds. Moreover, the apparatus of the present invention introduces no undesirable distortion insofar as the deilection fields themselves are concerned. It has been found, in general, that a magnetic shunt of certain types of high permeability material, if used as the shielding means, may have the effect of distorting the deflection field as by short circuiting the field across the rear windings of the yoke, thereby shifting the center of deflection. Additionally, it is known that, since conventional horizontal and vertical deflection rates are of the order of 15,750 kilocycles and 60 cycles per second, respectively, shielding against both frequency components of the deflection field may be performed in a frequency-selective manner.

With the foregoing in mind, the apparatus provided in accordance with the present invention and illustrated in Figures l and 3 will now be described. The yoke 26 is, as shown, conventionally housed in a cylindrical casing of insulating material such as Bakelite and is also enclosed at its rear end by a cap member 4S also formed of insulating material. The flux shielding apparatus of the present invention is conveniently supported by the cap 45 in the following manner. A dislf` i3 of copper or other non-magnetic material having high electrical conductivity is supported directly against the cap 45 by means of an eyelet Sti. In the interest or" completeness of description, it may be noted that the rear surface of the cap 45 is provided with raised annular ridges 52 which serve to prevent mechanical vibration of the disk 48 against the cap member. The disk 4S has, as shown, a central aperture of such size as to accommodate the neck 21 of the kinescope and should be of sufficient thickness to possess the necessary mechanical strength. Before describing the remaining portion of the shielding apparatus, it will be noted that a magnetic eld will produce eddy currents in a member of electrically conductive material which, in turn, will produce a reverse magnetic eld (Lenzs law) to oppose the field producing them. Since the production of eddy currents is the function of the frequency of the inducing field, it will be apparent that the disk 4S will be more greatly affected by the horizontal deflection eld than by the vertical field and will, therefore, be more eective as a shield against the higher frequency field.

Also supported by the cap member 45, through the agency of the eyelet 50, but spaced from the cap as by a grass cylindrical spacer 54 are two disk-like members 56 and 58 of grain-oriented silicon steel. The members 56, 58 are held in place by the upset end of the eyelet 5t), which eyelet may, for example, be formed of In the interest of4 providing a complete disclosure, it will be noted that the silicon steel members 56 and 53 may he formed of Tran-Cor (Armco Steel Corp.) XXX steel. The disklike members are also formed, as shown, with central apertures of sufhcient diameter to accommodate the neck of the kinescope. j

Before describing the action of the shield apparatus including the copper disk 48 and the grain-oriented steel disks 56 and 58, certain characteristics of the magnetic shielding materials should be noted. While the copper disk 48 does have a certain shielding effect insofar as the low frequency vertical deilectionflux is concerned, Vmeans for additionally shielding the vertical'de'- ection flux is required. A basic requirement for such additional shielding means is that the material employed have relatively high magnetic permeability. It has been found that most high permeability materials are more expensive that that employed in accordance with t-hepresent invention, are fragile and, therefore, subject to cracking and may also exhibit varying permeability in different portions of a disk formed thereof. ln order to overcome such factors, the present invention employs as the shield which acts in conjunction with the lcopper shield disk-like members of grain-.oriented steel. That is to say, grain-oriented steel has been found to possess a high degree of magnetic permeability in the direction ofthe grain. It will, therefore, be apparent that a single disk of such material, as disposed between the deflection yoke and convergence magnets and with the direction of its grain orientatio-n parallel to the lines of magnetic iuxv to be shielded, a high degree of such shielding could beobtained. lt has also been found, however, that such an arrangement is undesirable by reason of the fact that there would result a shortening of one of the-deilection elds with Arespect to the other, which selective shortening would have an undesirable distorting elect upon raster dedection and of a type which causes misconvergence of the electron beam components, particularly in the corners of the raster. Stated otherwise, the use of a single grain-oriented steel disk member for shielding would have a tendency to warp the deilection eld in the direction of the grain-orientation.

Hence, in accordance with the present invention, the grain-oriented steel disk members 56 and 58 are disposed relative to each other in such manner that their respective grain orientations are at right angles. That is to say, the disk 56 is maintained with respect to the disk 53 so that the direction of grain orientation of the former is perpendicular to the direction of the grain orientation of the latter. In order to simplify the assembling of the disks, they may be provided during manufacture with notches 56 and 58', respectively the notches being indicative of the direction of grain orientation. Thus, when the disks are assembled so that the notches of the disk 56 lie along a line which is at right angles to the notches S8 of the disk 58, the desired relative orientation of the disks is automatically achieved. The particular orientation of the disks with respect to the deflection yoke is, however, not critical.

By virtue of the employment of the two disks with their grain orientations at right angles to each other; the direction-sensitive permeability of either one of the disks is effectively eliminated, so that, `as Vthe `:disksp56 and 58 serve to shunt the deflection lux from the yoke, no undesirable direction-sensitive distortion is produced in the deection field. Moreover, the two disks in combination atiord a greater Adegree of shielding than that which a single disk of the same thickness can provide.

By virtue of the presence of the copper disk 48, the distance of the steel disks Se and 58 from the yoke is rendered less critical than would be the case in the absence of the copper disk. The length of the spacer elements 54 may be determined experimentally to suit the requirements of different situations involving different yoke structures and the like. In accordance with one specific arrangement successfully employed, the spacers 54 (four in number, for example) separate the disk 56 from the disk 4S by 5/15-inch. lthas been shown experimentally that the spacing of the steel disks from the yoke is rendered even less critical when the copper disk 4 8 .is Vof greater diameter than the steel disks, which `fact indicates that 'it is preferable to employ a copper .disk of greater diameter than the steel disks. It is also to be noted that the use of perpendicularly disposed, grainoriented steel disks precludes any undesirable foreshorten- 18 ing of the-`deection Ytielrlssuch'as would result in an undesired shift ofthe-respective 'horizontal and vertical deectionv centers, which Acenters should .coincide with the color centersffas lwill bemnderstood.

While the invention lhas been-described 'in accordance with a specific embodiment employing Vgrain-oriented silicon lsteel as the materiallof a pair of disk-like members disposed at right angles to each other, suitable medincations :may Abe .made in accordance with the principles oflthe invention. For example, `four such disk-like members arranged withftheir directions of grain orientation displaced`9l:may Ybe-employed to provide even greater shielding action. A

'Having fthus v"described ,my-invention, what-l claim as ynew :and desire to secure lby Letters Patent is:

l. ln a cathode-ray tube image reproducing system wherein an `electron .beam component which, after traversingl av predeflection :region fis angularly deflected both horizontally and verticallyuat substantially different rates by electromagnetic ybeam ldeflection apparatus to scan a rectangular raster; yapparatus located between said predeection region and Asaid electromagnetic apparatus for excluding deflection uX `.from said region, which comprises: apairof :grain-'oriented lsteel ydisk members mounted externally of said-tube andfha'vinga central aperture of suitable dimensions to :accommodate said tube, said disk members :being .disposed such that the directions of orinetation of :their .grain vstructures 4are substantially perpendicular.

v2. In fa .cathode-.ray itube image. -reproducing system wherein an electron-:beam component which, after traversing :a :pre-:deection Aregion Ais angularly deflected both horizontally and vertically Yat substantially different rates by .electromagnetic beam/deflection apparatus to scan a rectangular raster; Vapparatus located between said predeiiection region and Asaid electromagnetic apparatus for excluding vdelection -ux from Vsaid region, which` comprises: `:aidisk-like member vofinon-magnetic material having rhigh .electrical conductivity ,mounted externally of said tube landxhaving a central yaperture of suitable dimensionsto accommodate said tube; and first and second disk-like members ofgrain-oriented v steel mounted externally of said tube, each having ,a central aperture of suitable :dimensions :to accommodate said tube, said first and seconddis'kflike. membersy being located on the side of said rst :member :remote from said beam ldeilection apparatus land being disposed with their respective grain orientation directions Vat right angles ,to each other.

3. The' invention as defined. by claim 2 wherein said rstfnamed disk-like member fisgof greater external dimensionsradially ofgsaid tube ,than said steelmembers.

4. In a z'cathodefray :tube image ,reproducing system, whereinfan electron `beam component which, after traversing a pre-deflection region is angularly deilected both horizontally and-vertically :at 'substantially diterent rates by electromagnetic beam deflection apparatus to scan a rectangular raster; apparatus located between said predeilection region and said electromagnetic apparatus for excluding deection liux from said region, which comprises, vadisk-like member of non-magnetic material having high electrical conductivity mounted externally of said .tube ,and having a central aperture of suitable dimensions to Iacconnnodate said tube; and rst and second .disk-like 'members fof gram-oriented steel mounted externallyy offsaid.tubezandadisposed with their respective directions `of :grain :orientation at right angles to each other, :said disk-likcvsteel ,members being spaced Afrom andlocated ontheside of ,said firstmember remote from said :beam :deflection apparatus.

5: In a cathodefray ztube image-reproducing isystem wherein a plurality ,of electron beam components, which traverse pre-deflection,pathsthatare spaced respectively aboutthelongitudinal axis ,of .the tube, are angularly delected both horizontally .and vertically at high and low frequencies, respectively, by electromagnetic beam deection apparatus to scan a raster in a predetermined plane, electron beam convergence apparatus comprising, a plurality of electromagnets respectively mounted adjacent to said pre-deection beam paths and energizable to produce respective elds transverse to said beam paths, each of said electromagnets having a core includ` ing a body portion located externally of said tube and a pair of pole pieces located internally of said tube and respectively extending from points adjacent to opposite ends of said body portion into the region of said assoA ciated beam component; a non-magnetic shield of electrically conductive material located between said de ilection apparatus and said convergence electromagnets to exclude high frequency deection uX from said electromagnets; and a pair of shield members of grain-oriented steel located between said non-magnetic shield and said convergence electromagnets and disposed with their directions of grain orientation normal to each other.

6. Electron beam convergence apparatus as defined in claim 1 wherein, said non-magnetic shield and said magnetic shield comprise disk-like members.

7. Electron beam convergence apparatus as deiined in claim 6 wherein, said disk-like member of non-magnetic material is of greater dimension radially of said tube than said magnetic member.

S. Shielding apparatus for use in conjunction with an electromagnetic yoke of the type made up of horizontal and vertical deflection windings for producing electromagnetic deection elds of substantially diierent frequencies, said apparatus comprising: first and second disk-like members of grain-oriented magnetic material secured with their respective directions of `grain orientation at right angles to each other; and means for supporting said disklike members at one end of such yoke.

9. Shielding apparatus for use in conjunction with au electromagnetic yoke of the type made up of horizontal and vertical deection windings ror producing electromagnetic deection elds of substantially dierent frequencies, said apparatus comprising: a disk-like member of non-magnetic, electrically conductive material; rst and second disk-like members of grain-oriented magnetic material secured with their respective directions of grain orientation at right angles to each other; `and means for supporting said disk-like members at one end of such yoke.

10. An electromagnetic cathode ray beam deflection yoke which comprises: a pair of electromagnetic deection windings adapted to produce magnetic deection fields of substantially diierent frequencies; iirst and second disk-like members of grain-oriented steel `arranged with their respective directions of grain orientation at right angles to eac-h other; and means for supporting said disklike members at one end of said windings.

l1. An electromagnetic cathode ray beam deection yoke which comprises: a pair of electromagnetic deection windings adapted to produce magnetic deection fields of substantially diierent frequencies; -a disk-like member of non-magnetic, electrically conductive material; iirst and second disk-like members of grain-oriented steel arranged with their respective directions of grain orientation at right angles to each other; and means for supporting said disk-like members at one end of said windings, said electrically conductive member being located between said windings and said steel members.

References Cited in the file of this patent UNITED STATES PATENTS 2,234,720 De Tar Mar. 11, 1941 2,431,077 Poch Nov. 18, 1947 2,463,720 Schade Mar. 8, 1949 

